1. Field of the Invention
The present invention relates to an automatic disk discriminating method and apparatus in an optical disk system, and more particularly, to an automatic disk discriminating method and apparatus for discriminating between disk types by comparing a specific period value of a radio frequency (RF) signal reproduced from each disk with a predetermined reference value, after focus controlling.
Generally, in an optical disk system, when data stored in a disk are read, the focus spot of a laser beam radiated from an optical pickup should land on an exact spot of a disk and travel exactly along a guard groove or data pit so that precise and distortion-free signals are read. In a system of reproducing optical disks having the same physical structure, that is, the same substrate thickness, a reproduction method can be determined by reading out data in a lead-in region of the disk without discriminating between disk types.
However, in the case of a system which can reproduce disks having different physical structures such as a compact disk (CD) or a digital video disk (DVD), a stable servo operation is difficult to achieve and thus the disk types cannot be discriminated. If the disk types are not discriminated, further operations cannot be performed.
2. Description of the Related Art
FIG. 1 shows an optical disk system adopting a conventional disk discriminating apparatus utilizing the amplitude of an information signal to overcome the problem. The disk types can be discriminated by two methods in the disk discriminating apparatus shown in FIG. 1.
In the first disk discriminating method, after performing focusing and tracking control operations corresponding to the CD by a focus driver 116 and a track driver 117, an information signal is detected by a photodiode 112b and a current-to-voltage converter 112c. Subsequently, the amplitude of the information signal is detected by an information signal amplitude detector 113 and compared with a predetermined value by a comparator 114. Based on the compared result, the CPU 120 determines the switching position of the switch 121. Specifically, if the amplitude of the information signal is less than the predetermined value, the comparator outputs a signal (DVD) which signifies that the disk is a DVD. Then, the CPU 120 controls the switching position of the switch 121 such that a DVD loop in the servo signal processor 115 is active, and generates and outputs servo control signals for the DVD. Meanwhile, if the amplitude of the information signal is larger than the predetermined value, the comparator outputs a signal (CD) which signifies that the disk is a CD. Then, the CPU 120 maintains the switching position of the switch 121 such that a CD loop in the servo signal processor 115 is active, and generates and outputs servo control signals for the CD.
On the other hand, in the second method, information for discriminating the thickness of a substrate is extracted by performing focusing and tracking control operations corresponding to the CD. If a central processing unit (CPU) 120 recognizes that the thickness of the substrate corresponds to the DVD by use of the information, the apparatus is switched to a focusing control state for the DVD by the switch 121. In FIG. 1, the reference numerals 118, 119 and 123 indicate a voice coil motor (VCM) driver, a spindle driver and a spindle motor, respectively.
However, according to these methods, the disk type may be erroneously determined if there is noise in the information signal to change the amplitude of the information signal.